Recent estimates indicate that more than 19 million Americans over the age of 18 years experience a depressive illness each year. The American Psychiatric Association recognizes several types of clinical depression, including Mild Depression (Dysthymia), Major Depression, and Bipolar Disorder (Manic-Depression). Major Depression is defined by a constellation of chronic symptoms that include sleep problems, appetite problems, anhedonia or lack of energy, feelings of worthlessness or hopelessness, difficulty concentrating, and suicidal thoughts. Approximately 9.2 million Americans suffer from Major Depression, and approximately 15 percent of all people who suffer from Major Depression take their own lives. Bipolar Disorder involves major depressive episodes alternating with high-energy periods of rash behavior, poor judgment, and grand delusions. An estimated one percent of the American population experiences Bipolar Disorder annually.
Significant advances in the treatment of depression have been made in the past decade. Since the introduction of selective serotonin reuptake inhibitors (SSRIs), i.e., Prozac®, many patients have been effectively treated with anti-depressant medication. New medications to treat depression are introduced almost every year, and research in this area is ongoing. However, an estimated 10 to 30 percent of depressed patients taking an anti-depressant are partially or totally resistant to the treatment. Those who suffer from treatment-resistant depression have almost no alternatives. Thus, there is a need to develop alternative treatments for these patients.
The use of electrical stimulation for treating neurological disease, including such disorders as movement disorders including Parkinson's disease, essential tremor, dystonia, and chronic pain, has been widely discussed in the literature. It has been recognized that electrical stimulation holds significant advantages over lesioning since lesioning destroys the nervous system tissue. In many instances, the preferred effect is to modulate neuronal activity. Electrical stimulation permits such modulation of the target neural structures and, equally importantly, does not require the destruction of nervous tissue. Such electrical stimulation procedures include electroconvulsive therapy (ECT), repetitive transcranial (rTMS) magnetic stimulation and vagal nerve stimulation (VNS).
Efforts have been made to treat psychiatric disorders with peripheral/cranial nerve stimulation. Recently, partial benefits with vagus nerve stimulation in patients with depression have been described in U.S. Pat. No. 5,299,569. Another example of electrical stimulation to treat depression is described in U.S. Pat. No. 5,470,846, which discloses the use of transcranial pulsed magnetic fields to treat depression. Yet further, U.S. Pat. No. 5,263,480 describes that stimulation of the vagus nerve may control depression and compulsive eating disorders and U.S. Pat. No. 5,540,734 teaches stimulation of the trigeminal or glossopharyngeal nerves for psychiatric illness, such as depression.
Deep brain stimulation (DBS) has been applied to the treatment of central pain syndromes and movement disorders, and it is currently being explored as a therapy for epilepsy. For instance, U.S. Pat. No. 6,016,449 and U.S. Pat. No. 6,176,242 disclose a system for the electrical stimulation of areas in the brain for the treatment of certain neurological diseases such as epilepsy, migraine headaches and Parkinson's disease.
Various electrical stimulation and/or drug infusion devices have been proposed for treating neurological disorders. Some devices stimulate through the skin, such as electrodes placed on the scalp. Other devices require significant surgical procedures for placement of electrodes, catheters, leads, and/or processing units. These devices may also require an external apparatus that needs to be strapped or otherwise affixed to the skin.
However, despite the aforesaid available treatments, there are patients with major depression that remain treatment refractory and chronically disabled. For these severely ill and disabled patients, novel therapies are required.